Re: [PATCH 1/4] mm/slub: factor user tracking metadata size calculation

[Hao Li <hao.li@linux.dev>]

On Tue, Jun 16, 2026 at 10:14:07PM +0800, Pengpeng Hou wrote:
> SLAB_STORE_USER currently stores two struct track records in the per-object
> debug metadata.  The size is open-coded as 2 * sizeof(struct track) in
> several layout and offset calculations.
> 
> Add TRACK_NR and a small helper for the user-tracking metadata size.  This
> keeps all offset calculations tied to the number of track records and makes
> the following extension less error-prone.
> 
> No functional change.

Do we really need a user_tracking_size helper? This seems introducing some
redundant checking for SLAB_STORE_USER.

For example in set_orig_size(), obj_exts_offset_in_object() and
check_pad_bytes()

redundant checking may be confused...

> 
> Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
> ---
>  mm/slub.c | 25 ++++++++++++++++---------
>  1 file changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index f87e693aca5d..43d4febd5bf2 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -327,7 +327,15 @@ struct track {
>  	unsigned long when;	/* When did the operation occur */
>  };
>  
> -enum track_item { TRACK_ALLOC, TRACK_FREE };
> +enum track_item { TRACK_ALLOC, TRACK_FREE, TRACK_NR };
> +
> +static inline unsigned int user_tracking_size(slab_flags_t flags)
> +{
> +	if (flags & SLAB_STORE_USER)
> +		return TRACK_NR * sizeof(struct track);
> +
> +	return 0;
> +}
>  
>  #ifdef SLAB_SUPPORTS_SYSFS
>  static int sysfs_slab_add(struct kmem_cache *);
> @@ -751,7 +759,7 @@ static inline void set_orig_size(struct kmem_cache *s,
>  		return;
>  
>  	p += get_info_end(s);
> -	p += sizeof(struct track) * 2;
> +	p += user_tracking_size(s->flags);
>  
>  	*(unsigned long *)p = orig_size;
>  }
> @@ -767,7 +775,7 @@ static inline unsigned long get_orig_size(struct kmem_cache *s, void *object)
>  		return s->object_size;
>  
>  	p += get_info_end(s);
> -	p += sizeof(struct track) * 2;
> +	p += user_tracking_size(s->flags);
>  
>  	return *(unsigned long *)p;
>  }
> @@ -885,7 +893,7 @@ static unsigned int obj_exts_offset_in_object(struct kmem_cache *s)
>  	unsigned int offset = get_info_end(s);
>  
>  	if (kmem_cache_debug_flags(s, SLAB_STORE_USER))
> -		offset += sizeof(struct track) * 2;
> +		offset += user_tracking_size(s->flags);
>  
>  	if (slub_debug_orig_size(s))
>  		offset += sizeof(unsigned long);
> @@ -1088,7 +1096,7 @@ static void init_tracking(struct kmem_cache *s, void *object)
>  		return;
>  
>  	p = get_track(s, object, TRACK_ALLOC);
> -	memset(p, 0, 2*sizeof(struct track));
> +	memset(p, 0, user_tracking_size(s->flags));
>  }
>  
>  static void print_track(const char *s, struct track *t, unsigned long pr_time)
> @@ -1196,8 +1204,7 @@ static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p)
>  
>  	off = get_info_end(s);
>  
> -	if (s->flags & SLAB_STORE_USER)
> -		off += 2 * sizeof(struct track);
> +	off += user_tracking_size(s->flags);
>  
>  	if (slub_debug_orig_size(s))
>  		off += sizeof(unsigned long);
> @@ -1401,7 +1408,7 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p)
>  
>  	if (s->flags & SLAB_STORE_USER) {
>  		/* We also have user information there */
> -		off += 2 * sizeof(struct track);
> +		off += user_tracking_size(s->flags);
>  
>  		if (s->flags & SLAB_KMALLOC)
>  			off += sizeof(unsigned long);
> @@ -7820,7 +7827,7 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s)
>  		 * Need to store information about allocs and frees after
>  		 * the object.
>  		 */
> -		size += 2 * sizeof(struct track);
> +		size += user_tracking_size(flags);
>  
>  		/* Save the original kmalloc request size */
>  		if (flags & SLAB_KMALLOC)
> -- 
> 2.43.0
> 

-- 
Thanks,
Hao